1. Field of the Invention
The present invention relates to a pipe joint made of resin to be suitably used for a pipe used for a fluid which is a liquid having high purity or ultrapure water, or which is a fluid adapted to undergo a change in temperature. More specifically, the present invention provides a pipe joint made of resin capable of assuring both excellent sealing properties regardless of fluid temperature variations and good flowability enabling the fluid to smoothly flow in the pipe without remaining at the pipe joint.
2. Description of the Prior Art
There is known a pipe joint made of resin of the type above-mentioned, for example, as shown in FIG. 6. In FIG. 6, a cylindrical joint body A has a pipe receiving portion into which an insertion portion b1 at one end of a pipe B is to be inserted. The pipe receiving portion is provided at the inlet thereof with a sealing tapering portion a1, the diameter of which is gradually reduced in a direction toward the inside of the joint body A. An outer ring D is provided at the inner end thereof with a sealing portion d1 coming in contact with the sealing portion a1. The outer ring D is put immediately outside of the insertion portion b1 of the pipe B. This causes the pipe B to be locally pushed diametrically inward1y at b2.
An external thread portion a2 at one end of the joint body A is threaded1y connected to an internal thread portion el of a pushing ring E. By forwarding such threaded connection, the outer ring D is pushed toward the joint body A. This imparts a sealing force to the sealing portions a1 and d1.
Accordingly, the pipe B is regulated by the outer ring D so restricted as to be axially immovable by the joint body A and the pushing ring E. This prevents the pipe B from coming out from the joint body A. The inner surface of the outer ring D is pressingly contacted with the projecting portion b2 to generate a sealing force. This sealing force together with the sealing force at the sealing portions al and d1, prevents leakage of fluid to the outside in the pipe B and an entry of foreign matter into the pipe B.
However, the conventional pipe joint made of resin shown in FIG. 6 involves the likelihood that, with the passage of time, the projecting portion b2 of the pipe B experiences stress relaxation which lowers the sealing force between the inner surface of the outer ring D and the outer surface of, the projecting portion b2, resulting in deterioration of the sealing properties. This may provoke a micro-leakage of the fluid. Further, if the fluid has a high temperature, the pipe B is softened to accelerate the stress relaxation of the projecting portion b2. This results, in a short period of time, in a decrease in the sealing force between the inner surface of the outer ring D and the outer surface of the projecting portion b2, causing the fluid to leak.
There is also known a pipe joint as shown in FIG. 7. In FIG. 7, the joint body A has a pipe receiving portion into which an insertion portion b1 at one end of a pipe B is to be inserted. The pipe receiving portion is provided at the inlet thereof with a sealing tapering portion a1, the diameter of which diameter is gradually reduced in a direction toward the inside of the joint body A. An inner ring F has a peripheral wall f having a trapezoidal section, is pressingly inserted in the pipe B immediately inside of the insertion portion b1 thereof. This causes the pipe B to locally project diametrically outward1y at b3. An external thread portion a2 at one end of the joint body A is threadably connected to an internal thread portion e1 of a pushing ring E. By forwarding such threaded connection, the projecting portion b3 of the pipe B and the inner ring F are pushed toward the joint body A, so that the inclined surface of the projecting portion b3 is pushed to the sealing portion al to generate a sealing force.
Accordingly, the projecting portion b3 of the pipe B is held by and between the sealing portion a1 of the joint body A and a pressing portion e2 of the pushing ring E and the peripheral wall f of the inner ring F. This prevents the pipe B from coming out from the joint body A. Further, the inclined surface of the projecting portion b3 is pushed to the sealing portion a1 to generate a sealing force. This sealing force prevents a leakage to the outside of the fluid in the pipe B and an entry of foreign matter into the pipe B.
In the conventional pipe joint made of resin shown in FIG. 7, the spontaneous stress relaxation at an ambient temperature is less than that in the pipe joint shown in FIG. 6. Accordingly, the pipe joint in FIG. 7 provides sealing properties slightly higher than those provided by the pipe joint in FIG. 6. However, if the fluid has a high temperature, the inner ring F directly exposed to the fluid is apt to be easily softened. Accordingly, the stress relaxation of the inner ring F to decrease the pushing force exerted to, the projecting portion b3 of the pipe B becomes considerable. Thus, the sealing force is lost to cause the fluid to leak.
In addition to the problems above-mentioned, the pipe joints made of resin shown in FIGS. 6 and 7 present the following problems.
In each of the pipe joints in FIGS. 6 and 7, the flow path of the pipe B is not uniform in section. That is, the pipe B is locally reduced in diameter due to the projecting portion b1 or the inner ring F. This prevents the fluid from being smoothly moved. Particularly in the pipe joint in FIG. 7, there is formed a fine gap between the outer surface of the peripheral wall f of the inner ring F and the inner surface of the projecting portion b3. This causes the fluid to remain in this gap. Accordingly, the pipe joint in FIG. 7 is not suitable as a joint for a pipe used for a liquid having a high purity or ultrapure water of which smooth movement is required. This imposes restrictions on the use of such a pipe joint.